The objectives of this proposal are three-fold: 1. Develop Electron Spin Resonance for probing the interaction between chemical carcinogens and cellular constituents, primarily DNA, chromatin, and microsomal membranes. 2. Develop an assay using spin-labels for estrogen receptors in estrogen responsive tissues, particularly breast tumors. Probe the structural characteristics of these estrogen receptors during transformation from the cytosol to the nucleus. 3. Study the effects of lipid peroxidation on cytochrome P450 levels in microsomes and its role in carcinogenesis.